(1) Field of the Invention
The present invention relates to a hot-melt adhesive. More particularly, the present invention relates to a hot-melt adhesive having a novel composition, which is suitable for bonding such resins as olefin resins and olefin-vinyl alcohol copolymers.
(2) Description of the Prior Art
Among various thermoplastic resins, olefin-vinyl alcohol copolymers, especially an ethylene-vinyl alcohol copolymer, is one of resins most excellent in the barrier property (permeation resistance) to various gases such as oxygen and perfume components. This resin is, however, defective in that gas permeability is extremely increased under high humidity conditions, though the resin shows an excellent gas barrier property under low humidity conditions.
In order to moderate this defect, there has widely been adopted a method in which a moisture-resistant thermoplastic resin such as polyolefin is laminated on an olefin-vinyl alcohol copolymer layer and the resulting laminate is used in the form of a cup-shaped, bottle-shaped, tubular or filmy vessel. However, since there is no substantial hot adhesiveness between the olefin-vinyl alcohol copolymer and olefin type resin, lamination and bonding of both the resins are accomplished only by using an adhesive.
This adhesive should have an excellent adhesiveness to both the resins, and lamination and bonding can be accomplished very easily and a laminate should be formed by co-extrusion. In view of these requirements, it is desirable that the adhesive be thermoplastic and capable of hot bonding and hot molding. As the adhesive capable of satisfying these requirements, an adhesive composed of an acid-modified olefin resin formed by graft modification with an ethylenically unsaturated carboxylic acid or its anhydride or a resin composition containing this modified olefin resin has been known and this adhesive alone is used on an industrial scale. In the art, there has been a desire to produce a vessel having a much reduced thickness by draw molding or draw forming of a bonded laminated structure. Therefore, development of an adhesive capable of providing a stronger bonding has been desired in the art.